This invention relates generally to the electromagnetic testing of elongate objects such as cables, pipes, rods and the like and is concerned in particular with the detection of cross sectional area variations in a wire rope.
Steel hoist ropes are used in many applications for conveying personnel or material. Such ropes must be examined regularly to ensure that operational standards are consistently being maintained and to detect deterioration in the ropes before safety problems can arise.
Defects in a wire rope can be placed in one of three categories, namely cross sectional area variations, changes in the wire contact pattern of a rope which is made up from strands of wires wound in a particular pattern, and broken wires.
The invention is concerned primarily with the first mentioned characteristic namely cross sectional area variations in a rope. The strength of a wire rope is dependent on its cross sectional steel area and this can for example be reduced by normal wear and tear, corrosion, and stretch necking of a weak part.